Sedimenting elastic filaments in turbulent flows

We investigate the gravitational settling of a long, model elastic filament in homogeneous isotropic turbulence. We show that the flow produces a strongly fluctuating settling velocity whose mean is moderately enhanced over the still-fluid terminal velocity and whose variance has a power-law dependence on the filament's weight but is surprisingly unaffected by its elasticity. In contrast, the tumbling of the filament is shown to be closely coupled to its stretching and manifests as a Poisson process with a tumbling time that increases as a power law with the elastic relaxation time of the filament. Apart from elasticity, inertia, and gravitational acceleration, we have also considered the effect of bending stiffness and found that stiff filaments settle slower but tumble faster than fully flexible filaments.